1. Field of the Invention
The invention relates to a device for guiding electromagnetic waves from a wave guide, in particular a multi-band wave guide, to a transmission line, in particular a microstrip line, arranged at one end of the wave guide, comprising coupling means for mechanical fixation and impedance matching between the wave guide and the transmission line.
One problem for devices of that kind is to ensure a good transmission of electrical power in the wave guide to transmission line transition. Poor transition results in large insertion loss and this may degrade the performance of the whole module, e.g. a transceiver module.
2. Description of the Related Art
A device with a structure known in the prior art is shown in FIG. 9. There is shown a wave guide 10 and a transmission line 20, in particular a micro strip structure which are attached to each other for enabling transition of electromagnetic waves from the wave guide 10 to the transmission line 20. The transmission line 20 comprises a substrate 22 which is attached to a ground plane 24 for achieving good transition characteristics. The substrate 22 of the transmission line is typically made from low or high temperature co-fired ceramic LTCC or HTCC.
Impedance matching between the wave guide 10 and the transition line 20 is completed by providing a patch 26 in the transition area between the wave guide 10 and the transition line 20. Moreover, for improving impedance matching there is provided a separate slab 12 from dielectric material fastened within the wave guide 10. The slab 12 is, for example, attached within said wave guide 10 between machined shoulders 14.
The prior art approach for achieving impedance matching is based on a complex structure which can only be realised in a difficult and expensive manufacturing process. Moreover, quite often so-called back-shorts are used i.e. a metal part is attached behind the micro strip 20 opposite the opening of the wave guide 10 in order to achieve impedance matching. Attaching the back-short further increases the complexity of the structure.